Japanese Patent Application Publication No. 2005-278200 discloses an image reader having an angle sensor and a document detection sensor. The angle sensor detects a near-closed position where a cover is about to be closed and to cover a platen. The document detection sensor detects the document sheet when the cover is at the near-closed position. The size of the document sheet in the sub-scanning direction is determined using a result of detection by the document detection sensor. A reading section also detects the document sheet when the cover is at the near-closed position. The size of the document sheet in the main scanning direction is determined using a result of detection by the reading section. The image reader determines a size of the entire document sheet using the sizes of the document sheet in the sub-scanning direction and in the main scanning direction.